1. Field of the Invention
The present invention generally relates to a binocular telescope and more particularly relates to a binocular telescope which maintains the optical axes of a pair of optical systems thereof parallel with each other.
2. Description of The Related Art
As is well known, the distance between eyes of a person namely, the interpupillary distance varies with individual variations in age, sex and so on. Therefore, the binoculars require a mechanism for adjusting the distance between a pair of left and right lens-barrels, in order to adapt themselves to users of various interpupillary distances.
Among such interpupillary distance adjusting mechanisms, hitherto, there have been proposed various kinds of technical means of the type that adjust the interpupillary distance by moving a pair of left and right lens-barrels of a binocular telescope in parallel with each other.
As an example of such technical means, for example, the Japanese Patent Publication No. 60-46407/1985 Official Gazette describes a means for adjusting the distance between the optical axes of a pair of optical systems of a binocular telescope by placing a pair of left and right lens-barrels, which respectively hold the pair of optical systems, in such a manner that the pair of the optical axes become parallel with each other, and by further disposing a pair of front and rear guide rails or shafts in a direction perpendicular to the optical axes and by furthermore holding the left and right lens-barrels on these two guide shafts in such a manner as to be able to slide thereon. In this case, the front and rear guide shafts are illustrated in the drawing of this Official Gazette as being pressed throughout against and attached to a casing of an embodiment.
The technical means described in the Japanese Patent Publication No. 60-46407/1985 Official Gazette has a drawback in that the mechanism thereof cannot be compact in size and is a little too complex, as stated in the Japanese Patent Publication No. 60-48726/1985 Official Gazette. It is, thus, hard to say that this technical means is sufficiently durable if handled roughly.
In addition, in the case where a molding such as a plastic-molded member is employed as an armoring member, the armoring member deforms and the parallelism between the front and rear guide rails comes to be unable to be maintained if external force is applied thereto. Namely, in such a case, the parallelism between the optical axes of the optical systems respectively held by the left and right lens-barrels can not be sometimes maintained.
Further, as another example of a binocular telescope being capable of adjusting the interpupillary distance thereof, the Japanese Utility Model Publication No. 3-36974/1991 Official Gazette describes a binocular telescope having upper and lower frames for holding the left and right lens-barrels. In this telescope, a plurality of slits extending in a direction perpendicular to the optical axes of the optical systems are bored in one of the upper and lower frames. Further, an interpupillary-distance slide plate, in which guide pins slidably fitted to these slits are implanted, are slidably attached thereto in the longitudinal direction thereof. Moreover, the lens-barrels are mounted on this interpupillary-distance slide plate. Thereby, the lens-barrels are held by the frames in such manner as to be able to slide in a direction perpendicular to the optical axes of the optical systems.
The binocular telescope described in Japanese Utility Model Publication No. 3-36974/1991 Official Gazette has a structure in which a chassis (or frame) is mounted in a housing serving as the armoring member. Therefore, even if external force is exerted upon the armoring member, the parallelism between the optical axes of the left and right lens-barrels can be maintained by suitably setting the strength of this housing. This binocular telescope, however, has the serious drawbacks due to the provision of the chassis in that a further space becomes necessary in the binocular telescope and in that the weight and cost of the binocular telescope are increased.
Furthermore, as still another example of such a binocular telescope, the Japanese Patent Public Disclosure No. 4-116614 Official Gazette describes a binocular telescope in which a pair of left and right lens-barrels respectively containing optical systems are placed in such a manner as to be in parallel with each other, and in which a pair of front and rear guide shafts are placed to hold the pair of the left and right lens-barrels in such a manner that these lens-barrels can slide in a direction perpendicular to the optical axes of the optical systems, and in which each of the two front and rear guide shafts is supported on a base plate by using two columns.
The binocular telescope described in the Japanese Patent Public Disclosure No. 4-116614 Official Gazette, however, has a structure in which the base plate is provided and the parallelism between the optical axes of the optical systems is maintained by the stiffness of this base plate. This results an increase an space, weight and cost of the binocular telescope, similarly.